Multilayered Microhydraulic Actuators

ABSTRACT

An actuator with a stack of thin layers operates by electrowetting droplets between the layers. The actuator includes a first layer structure and a second layer structure positioned adjacent to the first layer structure. One or more liquid droplets are pinned to one of the layers and are positioned between the layers. The other layer includes electrodes. When the electrodes are energized, they electrostatically attract the liquid droplets to create relative motion between the two layers.

CROSS REFERENCE SECTION

This application is a continuation of U.S. utility application Ser. No.17/647,107 filed on Jan. 5, 2022 which claims priority to and benefit ofU.S. provisional Application No. 63/134,284 filed on Jan. 6, 2021, theentire contents of which are incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under FA8702-15-D-0001awarded by the U.S. Air Force. The government has certain rights in theinvention.

FIELD

This application relates to actuators and, more specifically, tomulti-layered microhydraulic actuators.

BACKGROUND

Electrostatic motors have traditionally suffered from high voltage andlow torque. The lack of a robust electrostatic motor technology is ofparticular concern in microsystems, because inductive motors do notscale well to small dimensions. Often microsystem designers must choosefrom a host of imperfect actuation solutions, leading to high voltagerequirements or low efficiency and thus straining the power budget of asystem.

Microelectromechanical (MEMS) motors can provide rotational actuation.At a micro-scale, higher driving frequency can increase power density,and smaller electrode gaps can reduce driving voltage. However, MEMSmotors have relatively low torque and the inability to scale in threedimensions due to their inherently thin nature

To address these challenges a desirable electrostatic motor technologyshould offer relatively low-voltage, relatively high-torque, relativelyhigh-efficiency, and the ability to scale.

SUMMARY

Microhydraulic actuators provide benefits such as relativelylow-voltage, relatively high-torque, relatively high efficiency, and theability to scale in thickness and in three dimensions. Microhydraulictechnology operates by electrically distorting equilibrium surfacetension state of attached liquid droplets with electrowetting. Thesedroplets can be chemically pinned to a structure. Then, electrostaticforces can be used to attract the droplets and move the structure tocreate actuation.

Using this concept, a microhydraulic motor can include multiplemicrohydraulic layers arranged in a stack with electrical connectionsbetween the multiple microhydraulic layers.

A multilayer microhydraulic motor provided in accordance with theconcepts as described herein may be capable of integrating forces fromthe multiple microhydraulic layers (e.g. two or more microhydrauliclayers). By utilizing multiple microhydraulic layers, actuators have adepth and a significant volume to generate force and mechanical power.This results in a microhydraulic motor capable of generating forceslarger than single layer microhydraulic motors. In embodiments, theachievable forces may be increased by up to three orders of magnitude ormore compared with prior art, single layer, microhydraulic motors.Consequently, the multilayer microhydraulic motors described herein maybe suitable for use in a wide variety of practical, real-worldapplications including, but are not limited to: robotic joints,optomechanical gimbals, unmanned arial vehicles (UAVs), medical devices,consumer electronics for foldable displays or haptic feedback,micro-assembly devices, and reconfigurable materials.

In an embodiment, an actuator that may provide some or all the benefitsand features described in this disclosure comprises: a first layerstructure; a second layer structure positioned adjacent to the firstlayer structure; and one or more liquid droplets positioned between thefirst layer structure and the second layer structure. The one or moreliquid droplets are pinned to the first layer. The actuator alsoincludes one or more electrodes positioned on the second layer andconfigured to move the first layer structure relative to the secondlayer structure by electrostatically attracting the one or more liquiddroplets pinned to the first layer structure.

One or more of the following features may be includes.

The liquid droplets may be conductive.

The liquid droplets may comprise water.

The liquid droplets may be surrounded by a layer of oil.

The layer structures may be disc-shaped and the actuator may be arotational motor.

The layer structures may comprise tracks and the actuator may be alinear motor.

The actuator may include a base layer structure configured to immobilizeeither the first layer structure or the second layer structure.

At least one of the liquid droplets may form electrical connectionsbetween the first layer structure and the second layer structure.

A control circuit may be coupled to the one or more electrodes andconfigured to selectively energize the one or more electrodes on onelayer to electrostatically attract the liquid droplets on an adjacentlayer.

The actuator may be a stepper motor and the control circuit may beconfigured to energize the one or more electrodes to step the firstlayer structure and the second layer structure relative to each other.

The control circuit may be electrically coupled to the electrodesthrough one or more of: the liquid droplets, a foldable flexibleinterconnect between the first layer structure and the second layerstructure, a via through the first layer and/or the second layer, and aconductive pin coupled to the first layer and/or the second layer.

In another embodiment, an actuator comprises a plurality of stackedlayer structures including: one or more first layer structures havingliquid droplets pinned to at least one side of the one or more firstlayer structures; and one or more second layer structures havingelectrodes pinned to at least one side of the one or more second layerstructures. The plurality of layer structures is stacked so that thesides of the layer structures having liquid droplets are facing thesides of the layer structures having electrodes. The actuator includes acontrol circuit electrically coupled to selectively energize at leastone electrode of the one or more second layer structures, to cause theat least one electrode to electrostatically attract at least one liquiddroplets of one or more first layer structures, to create relativemotion between the first layer structures and the second layerstructures.

One or more of the following features may be included.

The liquid droplets may comprise water.

The liquid droplets may be surrounded by a layer of oil.

The layer structures may be disc-shaped and the actuator may be arotational motor.

The layer structures may comprise tracks and the actuator may be alinear motor.

The actuator may include a base layer structure configured to immobilizeat least one layer structure of the plurality of layer structures.

The liquid droplets may form electrical connections between at leasttwo-layer structures of the plurality of layer structures.

The actuator may be a stepper motor and the control circuit may beconfigured to energize the one or more electrodes to step the layerstructures.

The control circuit may be electrically coupled to the electrodesthrough one or more of: the liquid droplets, a foldable flexibleinterconnect, a via through at least one of the layers of the pluralityof layers, and a conductive pin coupled to at least two layers of theplurality of layers.

The control circuit may be configured to cause at least some of thelayers to move in a same direction to increase a speed output of theactuator.

The control circuit may be configured to cause at least some of thelayers to move in opposite directions relative to each other to increasea torque output of the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the followingdescription of the drawings. The drawings aid in explaining andunderstanding the disclosed technology. Since it is often impractical orimpossible to illustrate and describe every possible embodiment, theprovided figures depict one or more exemplary embodiments. Accordingly,the figures are not intended to limit the scope of the invention. Likenumbers in the figures denote like elements.

FIG. 1 is a transparent isometric view of a rotational actuator.

FIG. 2 is an exploded view of the rotational actuator of FIG. 1 .

FIG. 3 is a cross-sectional view of stacked layers of an actuator.

FIG. 3A is a magnified view of a portion of the actuator of FIG. 3 .

FIG. 4 is a cross-sectional view of stacked layers of an actuator.

FIGS. 5A, 5B, and 5C are diagrams of a layer showing a droplet side andan electrode side.

FIG. 5D is a transparent, isometric view of a stack of layers showingelectrical connections between the layers.

FIG. 6A is an isometric view of a plurality of linear microhydraulicactuators configured to control motion of a ball camera.

FIG. 6B is an isometric view of a portion of a linear hydraulicactuator.

FIG. 7 is a diagram of a stack of layers illustrating relative motionbetween layers.

FIG. 8 is a diagram of another embodiment of a stack of layersillustrating relative motion between the layers.

FIG. 9 is a graph showing comparing characteristics of a microhydraulicactuator of this disclosure with an inductive motor and biologicalmuscles.

FIG. 10 is an isometric diagram of an embodiment of a microhydraulicactuator with foldable interconnects and a pin.

DETAILED DESCRIPTION

FIG. 1 is an isometric diagram of a rotational actuator 100 comprisingone or more disc-shaped layer structures 102. In the example ofembodiment of FIG. 1 a plurality of layers structures 102 a-102 g aredisposed in a stack 104. The actuator 100 further includes a housing 105having a top portion (or cap) 106 and a bottom portion (or base) 108 tohold the stack of layer structures (or “layers”) 104 in place. Theactuator 100 also includes an axle 110 (or motor shaft) which theactuator can rotate or otherwise move. The axle may optionally includeattachment structures (e.g. post 111) that can provide methods ofattaching the actuator to other mechanical elements. Control circuit 112is electrically coupled to one or more of the layers 102 to providepower and/or control the actuator's motion. For example, actuator 100may be a motor such as a stepper motor and the control circuit 112 cancontrol the rotation, direction of rotation, angular position (e.g. arotational angle at which the axle 110 is stopped), and rotational speedof the axle 110.

The control circuit 112 may be a single circuit or may comprise multiplecircuits to control the actuator 100. For example, the control circuit112 may include analog and digital circuits such as

-   -   logic circuits that control the signals provided to electrodes        of the actuator, power circuits that provide power to the        actuator, safety circuits, filters, and signal shaping circuits,        etc. In some embodiments, the control circuit 112 may be (or may        include) a programmable circuit such as a processor that can        execute software instructions stored in a memory, or        programmable hardware such as a field-programmable gate array        circuit.

FIG. 2 is an exploded view of the rotational actuator 100 of FIG. 1 . Inthis example, the layers 102 a and 102 c include. Holes 204 in themounting structures allow the layers 102 a and 102 c to be coupled(e.g., mounting structures 202 on their outer edge fastened or otherwisecoupled to a base layer 102 e and/or bottom portion 108. In thisconfiguration, layers 102 a and 102 c may be held stationary relative tothe bottom portion (or “base”) 108 while layers 102 f, 102 b, and 102 drotate. In other configurations, all the layers 102 may rotate relativeto the bottom portion 108. In general, depending on the gearing desiredin the actuator 100, any number of the layers 102 may be configured torotate or remain stationary relative to the base portion 108. Thesegearing configurations will be discussed in greater detail below. Ingeneral, including a greater number of layers may provide more flexibleoptions for gearing to adjust speed and torque output of the actuator.

The layers 102 may be formed from a rigid or semi-rigid material, suchas a thin plastic, a ceramic, a glass, a metal, a semiconductor, etc.For example, the layers 102 may be provided from polyimide having athickness less than about 1 mm, or less than about 0.01 mm thick. Thismay result in an actuator having a total thickness T that is 1 cm orsmaller, or 1 mm or smaller, or 0.5 mm or smaller.

In embodiments, the layers will include grooves (see FIG. 3 ) into whichare disposed liquid droplets and/or electrical traces that formelectrodes. Droplets of liquid on one or both surfaces of the layersseparate the layers and allow them to rotate with relatively lowfriction.

FIG. 3 is a cross-sectional view of a stack 302 of layers 304. The stack302 and layers 304 may be the same as or similar to the stack 104 oflayers 102 shown in FIGS. 1 and 2 . The stack 302 may include a baselayer 318 that may remain stationary with respect to the other layers304, and which defines one end of the stack. In embodiments, the baselayer is mechanically secured to a housing or other structure so that itremains stationary. The stack 302 may also include a top (or cap) layer320 that defines the opposite end of the stack.

In this example, the stack 302 includes five rotational layers (i.e.layers which may rotate or move around a central longitudinal axis 330):layers 304 a-d and top layer 320. In other embodiments, the stack 302may include less than five or more than five rotational layers. Inembodiments, the stack may comprise one or more rotational layers.

Each layer has first and second opposing surfaces. One or more of thelayers 304 may have a first surfaces (e.g. surface 306) having liquiddroplets (e.g. droplet 310) disposed or otherwise positioned thereon(and thus is sometimes referred to as a droplet surface). Inembodiments, the liquid droplets may be semi-spherical orsemi-cylindrical. In the example embodiment of FIG. 3 , surface 306 isprovided having one or more wells 315 in which droplets 316 aredisposed. In this example embodiment, wells 315 are formed via acombination of wall structures 317 and recesses or indentations 319(FIG. 3A). In embodiments, wells 315 may be provided from wallstructures alone or recesses alone (i.e. it is not necessary to use acombination of recesses and wall structures). The liquid droplets may bedisposed or positioned between layers and may be physically and/orchemically pinned to one of the layers. For example, liquid droplet 310is positioned between layer 304 a and layer 306 a. It is physicallyand/or chemically pinned within indentation 308 and wall structure 309of layer 304 a. The combination of indentation and wall structure mayprovide the liquid droplet with a height H which is greater that aheight which may be achieved using either the indentation or wallstructure alone and may provide stability so that the liquid droplet 310does not move relative to layer 304 a. However, the liquid droplet 310is not physically or chemically pinned to layer 304 b to allow layer 304b can move (e.g. rotate) relative to droplet 310 and layer 304 a. Ingeneral, the layers are formed from solid material, which may beflexible or rigid. The solid materials provide structure and are subjectto internal forces of the actuator. The liquid droplets providelubrication and motion, and act to provide electrostatic forces, asdescribed herein.

In embodiments, the droplet side 206 of the layer 304 a may comprisehydrophilic and hydrophobic solid surfaces, the hydrophilic areas wettedby the liquid droplets. The liquid droplets may comprise watercontaining 8 M LiCl, forming semi-cylindrical structured droplets.Uniform Laplace pressure may provide the shapes of the droplets.

In an embodiment, the rotational actuator may include two types ofdroplets: radial and circumferential, which may serve differentfunctions. As will be described below in conjunction with FIGS. 5A-5C.The radial (or “drive”) droplets (e.g. droplet 310) may besemi-cylindrical elongate droplets extending in a radial direction alongthe layers 304. The circumferential “rail” droplets may extendcircumferentially around areas of the layers 304 to form inner and outerrails, which may be used as conductors to carry electrical signals toand from the electrodes. At the edges of all droplets there may be astructure (e.g. a wall of polyimide) to increase droplet height andreduce viscous effects during actuation

One or more layers of oil 321 may be positioned around the liquiddroplets to retain the liquid droplets in place and/or to prevent theliquid droplets from evaporating.

The oil and the liquid droplets may also act as very low frictionlubricant and/or bearings between the layers. As a result, frictionbetween moving layers 304 in the stack 302 may be very low compared tofriction between moving parts in traditional actuators.

One or more of the layers 304 may also include a second surface (e.g.surface 312) having electrodes 314. The electrodes 314 may be formed inor on layer 304 a by printing, etching, or any other additive orsubtractive technique suitable for providing traces in or on asubstrate. The electrodes may be electrically coupled to and controlledby the control circuit 112 shown in FIGS. 1 and 2 . In general, theelectrodes of one layer (e.g. electrodes 314 of layer 304 a) may bedisposed or otherwise positioned so they are disposed over the liquiddroplets of an adjacent layer. In the example embodiment of FIG. 3 ,electrodes 314 are adjacent (or “facing”) droplets 316 disposed on layer320.

In embodiments, the layers 304 can self-align. After self-alignment thetranslational misalignment may be less than 1 μm, and rotationalmisalignment less than 0.03°. Self-alignment can be obtained throughpatterned hydrophilic structures on opposite layers that mate, or inanother technique through alignment pins.

FIG. 4 is a cross-sectional view of a stack 402 of layers 404. The stack402 and layers 404 may be the same as or similar to the stack 104 oflayers 102 shown in FIGS. 1 and 2 . The stack 402 may include baselayers and top layers, as described in conjunction with FIGS. 1-3 , butwhich are not shown in FIG. 4 . In this example, the stack 402 includesfive layers 404 a-e. However, in other embodiments, the stack mayinclude fewer or more than five layers.

Stack 402 may include a first type of layer having electrodes on bothsurfaces thereof. For example, layer 404 c has one or more electrodes406 on a first (or top) surface 408, and also one or more has electrodes410 on a second, opposite (or bottom) surface 412. Stack 402 may alsoinclude a second type of layer that has liquid droplets on both surfacesthereof. For example, layer 404 d has liquid droplets 414 on a first (ortop) surface 416 and liquid droplets 418 on a second, opposite (orbottom) surface 420. Regions (or spaces) 421 between the liquid dropletsand the layers may be filled with oil 422 that surrounds the liquiddroplets and, in conjunction with the liquid droplets, creates alow-friction interface between adjacent layers.

In this arrangement, the first type of layer with electrodes on bothsides (e.g. layers 404 a, 404 c, and 404 e) and the second type oflayers with liquid droplets on both sides (e.g. layers 404 b and 404 d)are stacked in an alternating fashion so that the liquid droplets arepositioned or otherwise disposed between each pair of adjacent layers.

FIGS. 5A, 5B, and 5C show a detailed top and bottom view of layer 502.Layer 502 is a layer with a first side having liquid droplets and asecond, opposite side having electrodes. Thus, layer 502 may be the sameas or similar to the layers 304 a-d shown in FIG. 3 . FIG. 5B is anenlarged image of the droplet side of area 504 and FIG. 5C is anenlarged image of the electrode side of area 504 of the layer 502.

Referring to FIG. 5A, the first, droplet side of layer 502 may includean array of radial grooves 506 that each hold a liquid droplet. Theradial grooves (and the droplets) may extend radially over a portion 508of the radius, or along the entire length of the radius, of the layer502 to create a ring 510.

The layer 502 may also have one or more circumferential rails thatinclude grooves 512-516 positioned around the radial grooves 506. Thecircumferential grooves 512-516 may retain conductive liquid dropletsthat act as fluidic, electrical rails to carry signals to theelectrodes. The rails may include one or more fluid vias 518 that allowmotor brushes 520 to make electrical connections with the fluid withinthe rail as the brushes 520 pass over the vias 518.

The rails in FIG. 5B are positioned outside the outer circumference ofring 510. However, in embodiments, similar rails may be positioned onlayer 502 inside the inner circumference of ring 510.

FIG. 5C shows the second, opposite side of layer 502, which includes oneor more electrodes 522. The electrodes 522 may be electrically coupledto motor brushes 520 so that, as the brushes receive power from thecontrol circuit, the electrodes become electrically charged. Inembodiments, the electrodes 522 may become electrically charged when thebrushes 520 pass over fluid vias 518 and meet the circumferential,conductive water droplets 512-516, forming an electrical connectionbetween the conductive water droplets and the brushes.

FIG. 5D is a diagram showing the electrical power distribution networkfor a linear multilayer microhydraulic actuator (e.g. a linear motor).As mentioned above, electrical power may be distributed to some or allthe layers in a stack. In embodiments, a liquid interconnect is used.Current (e.g. alternating current) flows from the base up through thefluidic rails 550 and vias 552, to the brushes 554, then to the driveelectrodes 556. It then couples to the drive droplets in the layer aboveor below and returns through the fluidic rails and vias back to thebase.

Path 558 illustrates the electrical power delivery path 558 through theactuator. Signals enter from a connector at the base, connect with ametal via to the brush electrodes, capacitively couple to the water 8MLiCl rails through an electrical double layer, ionically conduct throughthe fluidic rails and vias to Pt brush electrodes in each layer,transfer through a metal via to the Al drive electrodes, couplecapacitively to the drive droplets to form the electrowetting capacitor,then return though the 8 M LiCl reference rail into the brush electrodesin the base, and return to the connector.

In embodiments, a flexible, foldable interconnect may also provideelectrical connectivity between the layers. The interconnect may beformed from a flexible material, such as a thin plastic film, and mayinclude one or more conductive elements. Conductive pins coupled betweenlayers may also be used to provide electrical conductivity between thelayers.

In the embodiment shown in FIGS. 5A-C, the electrodes may have anelongate shape and may extend in a radial direction, like the liquiddroplets 506. This arrangement may be beneficial for a rotationalactuator. However, in other embodiments, the liquid droplets and/orelectrodes may have other shapes and be arranged in other positionsdepending on the type of actuator and motion desired.

For example, FIGS. 6A and 6B show a microhydraulic actuator configuredto rotate a ball camera (e.g. artificial eye) 602. FIG. 6A is anexploded view of a stack 603 of semi-circular layers 604, and anotherstack 606 of semi-circular layers 608. When the stacks 603 and 606 areassembled, they create a track-shaped actuator that can rotate the ballcamera 605. Additional stacks 610 and 612 may be added to rotate theball camera in six degrees of freedom.

In this example, the stacks create a rail or track that can be used tomove or rotate an object along the track. In general, the stacks can bemanufactured in any desired shape to create rotary actuators, linearactuators, or actuators of any other shape and motion in addition to therotary and track actuators described above.

Operation

The actuators described above operate by creating electrostatic (i.e.Coulomb) forces between the electrodes and the liquid droplets. When theelectrode is energized, it creates an electrical field. The electricalfield generates an electrostatic attractive force between the electrodeand the liquid droplet. That force pulls the electrode and the droplettoward each other and moves the respective layers, creating theactuator's motion.

FIG. 7 is a cross-sectional diagram of three layers of an actuator,illustrating the operation of the electrostatic forces. In this example,assume that base layer 702 remains stationary and that layers 704 and708 move relative to base layer 702.

As illustrated, base layer 702 includes a droplet side 710 and at leasttwo droplets 712, 714. Layer 704 includes an electrode side shown witheight electrodes 716, 718, 720, 722, 724, 726, 728, and 730; and adroplet side having droplets 732 and 734. Similarly layer 708 has anelectrode side shown with eight electrodes 736, 738, 740, 742, 744, 746,748, 750; and a droplet side having droplets 752 and 754.

To create the motive force, electrodes 716 and 724 are activated with apositive charge. The positive charge of the electrodes induces anegative charge in the nearby areas of droplets 714 and 712. These twoopposing charges create attractive, electrostatic forces indicated byarrows 756 and 758. The forces pull the layers together and, as aresult, layer 704 moves in the direction of arrow 760.

Similarly, an attractive force can be achieved by activating theelectrodes with a negative charge. For example, in this example,electrodes 736 and 744 are activated with a negative charge, whichinduces a positive charge in nearby liquid droplets 734 and 732,respectively. These opposing charges also create attractive,electrostatic forces indicated by arrows 762 and 764. The forces pulllayers 704 and 708 together and, as a result, layer 708 moves in thedirection of arrow 766.

In embodiments, multiple phases may be used to create continuous motionof the layers. Assume that electrodes 736, 738, 740, and 742 areactivated in four subsequent phases. Electrode 736 is activated firstand pulls layer 708 left relative to layer 704. Then electrode 736 isturned off and electrode 738 is activated and pulls layer 708 furtherleft relative to layer 704. Next, electrode 738 is turned off andelectrode 740 is activated and pulls layer 708 further left relative tolayer 704. In the fourth phase, electrode 740 is turned off andelectrode 742 is activated and pulls layer 708 yet further left relativeto layer 704. Then the four phases can be repeated with a new set offour actuators (e.g. actuators 744-750) that come in proximity withdroplet 734. In this way, the electrodes can be activated so that theactuator acts like a stepper motor. One skilled in the art willrecognize that, by actuating the electrodes in different patterns, thecontrol circuit can precisely control speed, position, and direction ofeach layer.

In this example, both layers 704 and 708 are rotating to the left, i.e.in the direction of arrows 760 and 766, while base layer 702 isstationary. Accordingly, the speed of each layer's rotation is based onthe frequency of the phases, and on the speed of the adjacent layer. Forexample, layer 704 is rotating with an angular velocity of θ relative tobase layer 702. Assuming the phases of electrode activation on bothlayers are the same, top layer 708 is rotating with a speed of θrelative to middle layer 704. Thus, top layer 708 is rotating with aspeed 2θ relative to bottom layer 702. Additional layers added on top oflayer 708 and rotating in the same direction may have increased speed.For example, a fourth layer added on top of layer 708 may rotate with anangular velocity of 3θ relative to bottom layer 702, a fourth layer mayrotate with an angular velocity of 4θ, etc.

Referring to FIG. 8 , the frequency and direction of the phases of theelectrodes can be changed to change the speed and/or torque output ofthe actuator. In this example, an additional layer is shown toillustrate the concept.

In layer 704, the four-phase electrode activation may be reversed sothat electrodes 730 and 722 are activated first, then electrodes 728 and720, then electrodes 726 and 718, and then electrodes 724 and 716. As aresult, the motion of layer 704 with respect to base layer 702 is alsoreversed, resulting in layer 704 moving to the right (as indicated byarrow 768), with a velocity of θ in the direction of arrow 768. Layer708 is configured to more to the left, as indicated by arrow 766. Andlayer 802 is configured to move to the right, as indicated by arrow 804.

In this example, because the direction of some of the layers isreversed, the angular velocity of layer 704 is θ (in the direction ofarrow 768) relative to the base layer 702, the angular velocity of layer708 is zero relative to the base layer 702, and the velocity of layer802 is θ (in the direction of arrow 804) relative to layer 702. In otherwords, in this example, every other row has a velocity θ, and thealternate rows have a velocity of zero relative to the base layer.However, the torque produce by layer 802 is increased relative to thetorque produced by layer 704. If, for example the torque produced bylayer 704 is τ, the torque produced by layer 802 may be 2τ.

The examples shown in FIGS. 7 and 8 include three and four layers,respectively. Of course, the actuators presented in this disclosure canhave any arbitrary number of layers; they are not limited to three orfour layers as shown in these examples. Thus, depending on theconfiguration, the velocity of the layers and the torque of the actuatorcan be configured to any arbitrary velocity and torque within themechanical confines of the particular actuator's configuration.

The figures in this disclosure, including FIGS. 7 and 8 , may not bedrawn to scale. For example, in FIGS. 7 and 8 , there is a gap betweensets of actuators (e.g. gap 806 between electrodes 722 and 724). Thisgap is shown for ease of illustrating multi-phase actuator activationand is not necessarily present in embodiments of the actuator. Ofcourse, some actuator configures may include gaps between some or allelectrodes depending on the actuator configuration.

The speed and torque configurations described above are a subset ofpossible layer arrangements. In general, a multilayer stack can compriseM regular, and N inverted electrode order layers, alternating up throughthe actuator. Alternatively, the forward and reverse layers need notalternate. An actuator may have multiple forward direction layers andmultiple reverse-direction layers in any order. The ability to provideconfigurations with different gear ratios, i.e. different speed and/ortorque configurations described above, may be beneficial formicro-actuator applications where the disclosed microhydraulic actuatorsmay provide gearing solutions that are more efficient, smaller, andlighter than traditional actuator solutions.

FIG. 9 is a plot of maximum unloaded angular velocity and blocked torquedensity for various rotational actuators. Inductive motors tend to havea high speed at low torque density, while microhydraulic motors andbiological joints tend to have a low velocity and a high torque density.Different M layer configuration can exchange speed for torque. Themicrohydraulic actuators that were measured for this chart had dropletswith 40 μm pitch, while 15 μm droplet pitch devices are projected fromscaling trends.

FIG. 10 is an isometric view of an embodiment of a microhydraulicactuator 1000 with foldable layers. Actuator 1000 may have a pluralityof stator layers 1002, 1004, 1006, etc. The stator layers may beconnected by one or more interconnection elements 1008, which connect tothe stator layers via a hinge (e.g. hinges 1010, 1012). Each statorlayer 1002, 1004, 1006 may be associated with a movable rotor layer(e.g. rotor layer 1014) which may be rotatably coupled to the statorlayer. As described above, the rotor layer may include a plurality ofliquid droplets that can be used to create actuator motion. The statorlayers may include one or more electrodes that can generateelectrostatic force between the electrodes and the liquid droplets, asdescribe above, to generate actuator motion.

In embodiments, the stator layers (e.g. 1002, 1004) and theinterconnection elements (e.g. 1008) may include conductors (not shown)etched or embedded thereon that provide electrical interconnectivitybetween the layers. The conductors can carry power and/or controlsignals between the layers and to/from the control circuit.

Additionally or alternatively, the stator layers may include one or moreholes or vias (such as via 1016) through which one or more conductivepins (such as pin 1018) can be inserted. The conductive pins 1018 mayprovide electrical connectivity and carry power and/or control signalsbetween the layers and to/from the control circuit.

Various embodiments of the concepts, systems, devices, structures andtechniques sought to be protected are described herein with reference tothe related drawings. Alternative embodiments can be devised withoutdeparting from the scope of the concepts, systems, devices, structuresand techniques described herein. It is noted that various connectionsand positional relationships (e.g., over, below, adjacent, etc.) are setforth between elements in the above description and in the drawings.These connections and/or positional relationships, unless specifiedotherwise, can be direct or indirect, and the described concepts,systems, devices, structures and techniques are not intended to belimiting in this respect. Accordingly, a coupling of entities can referto either a direct or an indirect coupling, and a positionalrelationship between entities can be a direct or indirect positionalrelationship.

As an example of an indirect positional relationship, references in thepresent description to disposing or otherwise positioning element “A”over element “B” include situations in which one or more intermediateelements (e.g., element “C”) is between elements “A” and elements “B” aslong as the relevant characteristics and functionalities of elements “A”and “B” are not substantially changed by the intermediate element(s).

Also, the following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprise,” “comprises,” “comprising, “include,” “includes,”“including,” “has,” “having,” “contains” or “containing,” or any othervariation thereof, are intended to cover a non-exclusive inclusion. Forexample, an apparatus, a method, a composition, a mixture or an article,that comprises a list of elements is not necessarily limited to onlythose elements but can include other elements not expressly listed orinherent to such apparatus, method, composition, mixture, or article.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance, or illustration. Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “one or more”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection”.

References in the specification to “embodiments,” “one embodiment, “anembodiment,” “an example embodiment,” etc., indicate that the embodimentdescribed can include a particular feature, structure, orcharacteristic, but every embodiment may or may not include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to affect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

For purposes of the description hereinafter, relative or positionalterms including but not limited to the terms “upper,” “lower,” “right,”“left,” “vertical,” “horizontal, “top,” “bottom,” and derivativesthereof shall relate to the described structures and methods, asoriented in the drawing figures. The terms “overlying,” “atop,” “on top,“positioned on” or “positioned atop” mean that a first element, such asa first structure, is present on a second element, such as a secondstructure, where intervening elements such as an interface structure canbe present between the first element and the second element. The term“direct contact” means that a first element, such as a first structure,and a second element, such as a second structure, are connected withoutany intermediary elements.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value. The term“substantially equal” may be used to refer to values that are within±20% of one another in some embodiments, within ±10% of one another insome embodiments, within ±5% of one another in some embodiments, and yetwithin ±2% of one another in some embodiments.

The term “substantially” may be used to refer to values that are within±20% of a comparative measure in some embodiments, within ±10% in someembodiments, within ±5% in some embodiments, and yet within ±2% in someembodiments. For example, a first direction that is “substantially”perpendicular to a second direction may refer to a first direction thatis within ±20% of making a 90° angle with the second direction in someembodiments, within ±10% of making a 90° angle with the second directionin some embodiments, within ±5% of making a 90° angle with the seconddirection in some embodiments, and yet within ±2% of making a 90° anglewith the second direction in some embodiments.

In this disclosure, the term actuator refers to a component or devicethat causes motion and control by creating motion of one or more partsof a machine. Actuators include, but are not limited to, motors. In thisdisclosure, the terms actuator and motor are sometimes usedinterchangeably.

It is to be understood that the disclosed subject matter is not limitedin its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The disclosed subject matter is capable ofother embodiments and of being practiced and carried out in variousways.

Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting. As such, those skilled in the art will appreciatethat the conception, upon which this disclosure is based, may readily beutilized as a basis for the designing of other structures, methods, andsystems for carrying out the several purposes of the disclosed subjectmatter. Therefore, the claims should be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the disclosed subject matter.

Although the disclosed subject matter has been described and illustratedin the foregoing exemplary embodiments, it is understood that thepresent disclosure has been made only by way of example, and thatnumerous changes in the details of implementation of the disclosedsubject matter may be made without departing from the spirit and scopeof the disclosed subject matter.

Accordingly, it is submitted that that scope of the patent should not belimited to the described implementations but rather should be limitedonly by the spirit and scope of the following claims.

All publications and references cited herein are expressly incorporatedherein by reference in their entirety

Various embodiments of the concepts, systems, devices, structures, andtechniques sought to be protected are described above with reference tothe related drawings. Alternative embodiments can be devised withoutdeparting from the scope of the concepts, systems, devices, structures,and techniques described. It is noted that various connections andpositional relationships (e.g., over, below, adjacent, etc.) may be usedto describe elements in the description and drawing. These connectionsand/or positional relationships, unless specified otherwise, can bedirect or indirect, and the described concepts, systems, devices,structures, and techniques are not intended to be limiting in thisrespect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship.

As an example of an indirect positional relationship, positioningelement “A” over element “B” can include situations in which one or moreintermediate elements (e.g., element “C”) is between elements “A” andelements “B” as long as the relevant characteristics and functionalitiesof elements “A” and “B” are not substantially changed by theintermediate element(s).

Also, the following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. The terms“comprise,” “comprises,” “comprising, “include,” “includes,”“including,” “has,” “having,” “contains” or “containing,” or any othervariation are intended to cover a non-exclusive inclusion. For example,an apparatus, a method, a composition, a mixture or an article, thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such apparatus, method, composition, mixture, or article.

Additionally, the term “exemplary” is means “serving as an example,instance, or illustration. Any embodiment or design described as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “one or more”and “at least one” indicate any integer number greater than or equal toone, i.e. one, two, three, four, etc. The term “plurality” indicates anyinteger number greater than one. The term “connection” can include anindirect “connection” and a direct “connection”.

References in the specification to “embodiments,” “one embodiment, “anembodiment,” “an example embodiment,” “an example,” “an instance,” “anaspect,” etc., indicate that the embodiment described can include aparticular feature, structure, or characteristic, but every embodimentmay or may not include the particular feature, structure, orcharacteristic. Moreover, such phrases are not necessarily referring tothe same embodiment. Further, when a particular feature, structure, orcharacteristic is described in connection with an embodiment, it mayaffect such feature, structure, or characteristic in other embodimentswhether or not explicitly described.

Relative or positional terms including, but not limited to, the terms“upper,” “lower,” “right,” “left,” “vertical,” “horizontal, “top,”“bottom,” and derivatives of those terms relate to the describedstructures and methods as oriented in the drawing figures. The terms“overlying,” “atop,” “on top, “positioned on” or “positioned atop” meanthat a first element, such as a first structure, is present on a secondelement, such as a second structure, where intervening elements such asan interface structure can be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary elements.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another, or atemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value. The term“substantially equal” may be used to refer to values that are within±20% of one another in some embodiments, within ±10% of one another insome embodiments, within ±5% of one another in some embodiments, and yetwithin ±2% of one another in some embodiments.

The term “substantially” may be used to refer to values that are within±20% of a comparative measure in some embodiments, within ±10% in someembodiments, within ±5% in some embodiments, and yet within ±2% in someembodiments. For example, a first direction that is “substantially”perpendicular to a second direction may refer to a first direction thatis within ±20% of making a 90° angle with the second direction in someembodiments, within ±10% of making a 90° angle with the second directionin some embodiments, within ±5% of making a 90° angle with the seconddirection in some embodiments, and yet within ±2% of making a 90° anglewith the second direction in some embodiments.

The disclosed subject matter is not limited in its application to thedetails of construction and to the arrangements of the components setforth in the following description or illustrated in the drawings. Thedisclosed subject matter is capable of other embodiments and of beingpracticed and carried out in various ways.

Also, the phraseology and terminology used in this patent are for thepurpose of description and should not be regarded as limiting. As such,the conception upon which this disclosure is based may readily beutilized as a basis for the designing of other structures, methods, andsystems for carrying out the several purposes of the disclosed subjectmatter. Therefore, the claims should be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the disclosed subject matter.

Although the disclosed subject matter has been described and illustratedin the foregoing exemplary embodiments, the present disclosure has beenmade only by way of example. Thus, numerous changes in the details ofimplementation of the disclosed subject matter may be made withoutdeparting from the spirit and scope of the disclosed subject matter.

Accordingly, the scope of this patent should not be limited to thedescribed implementations but rather should be limited only by thespirit and scope of the following claims.

All publications and references cited in this disclosure are expresslyincorporated by reference in their entirety

1. A actuator comprising: a first layer structure; a second layerstructure disposed over the first layer structure; one or more liquiddroplets positioned between a surface of the first layer structure and asurface of the second layer structure, wherein the one or more liquiddroplets are pinned to the first layer; and one or more electrodespositioned on the second layer and configured to provide anelectrostatic charge to the one or more liquid droplets pinned to thefirst layer structure.
 2. The actuator of claim 1 wherein the one ormore electrodes are configured to move the first layer structurerelative to the second layer structure by electrostatically attractingthe one or more liquid droplets pinned to the first layer structure. 3.The actuator of claim 1 wherein the liquid droplets are electricallyconductive.
 4. The actuator of claim 3 wherein the liquid dropletscomprise water.
 5. The actuator of claim 3 further comprising a layer ofoil disposed about the one or more liquid droplets.
 6. The actuator ofclaim 1 wherein the liquid droplets have a semi-cylindrical shape or asemi-spherical shape.
 7. The actuator of claim 1 wherein the layerstructures are disc-shaped and the actuator is a rotational motor. 8.The actuator of claim 1 wherein the layer structures comprise tracks andthe actuator is a linear motor.
 9. The actuator of claim 1 wherein atleast one of the liquid droplets forms an electrical connection betweenthe first layer structure and the second layer structure.
 10. Theactuator of claim 1 further comprising a control circuit coupled to theone or more electrodes and configured to selectively energize the one ormore electrodes on one layer to electrostatically attract the liquiddroplets on an adjacent layer.
 11. The actuator of claim 10 wherein theactuator is a stepper motor and the control circuit is configured toenergize the one or more electrodes to cause the first layer and/or thesecond layer to move in discrete steps.
 12. The actuator of claim 10wherein the control circuit is electrically coupled to the electrodesthrough one or more of: the liquid droplets, a flexible interconnectbetween the first layer structure and the second layer structure, a viathrough the first layer and/or the second layer, and a conductive pincoupled to the first layer and/or the second layer.
 13. An actuatorcomprising: a plurality of stacked layer structures including: one ormore first layer structures having liquid droplets pinned to at leastone side of the one or more first layer structures; one or more secondlayer structures having electrodes coupled to at least one side of theone or more second layer structures; wherein the plurality of layerstructures is stacked so that the sides of the layer structures havingliquid droplets are facing the sides of the layer structures havingelectrodes; and a control circuit electrically coupled to selectivelyenergize at least one electrode of the one or more second layerstructures to induce an electrostatic charge in at least one of theliquid droplets.
 14. The actuator of claim 13 wherein the controlcircuit is configured to energize the at least one electrode toelectrostatically attract the at least one of the liquid droplets tocreate relative motion between the first layer structures and the secondlayer structures.
 15. The actuator of claim 13 wherein the liquiddroplets are electrically conductive.
 16. The actuator of claim 15wherein the liquid droplets comprise water.
 17. The actuator of claim 15wherein the liquid droplets are surrounded by a layer of oil.
 18. Theactuator of claim 13 wherein the layer structures are disc-shaped andthe actuator is a rotational motor.
 19. The actuator of claim 13 whereinthe layer structures comprise tracks and the actuator is a linear motor.20. The actuator of claim 13 further comprising a base layer structureconfigured to immobilize at least one layer structure of the pluralityof layer structures.